1. Field of the Invention
The present invention relates to an ink droplet jet device, and more particularly to an ink droplet jet device utilizing deformation of a piezoelectric transducer.
2. Description of the Related Art
An ink droplet jet device is conventionally utilized in a piezoelectric ink jet printer head. In such a printer head, a volume of an ink channel is changed by a change in dimension of a piezoelectric transducer, and ink in the ink channel is jetted from an ink outlet nozzle. That is, when the volume in the ink channel is decreased, ink in the ink channel receives a positive pressure and is jetted from the nozzle, while when the volume is increased, ink receives a negative pressure and is introduced through a valve from an ink supplying portion into the ink channel. This type of ink droplet jet device is called a drop on-demand system. In such a device, a plurality of such jet units are arranged close to one another, and ink is jetted from each nozzle communicating with each ink channel to correspond to an image signal, thus forming desired characters and images on a recording medium such as paper.
This kind of ink droplet jet device is described, for example, in U.S. Pat. Nos. 4,879,568 and 4,887,100.
First, a construction of an ink channel array of the conventional ink droplet jet device is described with reference to FIGS. 4 and 5. FIG. 4 is a sectional view of an array constituting a part of the conventional droplet jet device. FIG. 5 is a perspective view illustrating a manufacturing method of an array constituting a part of the conventional ink droplet jet device.
The array of the conventional droplet jet device comprises a piezoelectric ceramic plate 101, a cover plate 121, a plurality of electrodes 111A-D and a nozzle plate 141.
The piezoelectric ceramic plate 101 is polarized in a direction of an arrow 151 and has a plurality of side walls 102. A groove 103 is formed between the pair of side walls 102, which is an ink channel as mentioned below. The groove 103 has a rectangular shape and has a width of about 80 .mu.m (micro-meter), a height of about 200 .mu.m and a length of about 10 mm.
The cover plate 121 is formed of a metal material, glass material or ceramic material. The cover plate 121 is bonded on the upper surface 104A of the piezoelectric ceramics plate 101, that is on the upper surface of the plurality of side walls 102 by an adhesive layer 112 such as epoxy adhesive. With this construction, a plurality of ink channels 131A-D are formed so as to be spaced from one another in a lateral direction. Each ink channel has a rectangular shape having a rectangular cross section. As shown in FIG. 5, each side wall 102 extends over a full length of each ink channel 131A-D, and is deformable in the direction perpendicular to an axis of each ink channel and the polarizing direction 151. The volume in the ink channel 131 is changed by the deformation of each side wall 102, so that an ink pressure in any of the ink channels 131A-D can be changed.
The metal electrodes 111A-D for generating a driving electric field are formed on a surface of each side wall 102. The metal electrodes 111A-D are surface-treated to prevent corrosion thereof by the ink.
The nozzle plate 141 is a plate formed, for example, by a nickel electroforming, and is fixed to one end surface 104B of the piezoelectric ceramic plate 101 and the cover plate 121. A plurality of ink outlets, that is jet nozzles 142, are arranged in the nozzle plate 141, such that the jet nozzles 142 communicate with each of ink channels 131A-D in one-to-one correspondence to each other. A hole diameter of the jet nozzle is, for example, 30 .mu.m, and a distance between centers of the jet nozzles is 160 .mu.m. The ink which receives a positive pressure by the deformation of each ink channel 131A-D is jetted from the jet nozzle 142.
Next, the operation of the array constituting a part of the conventional ink droplet jet device is described with reference to FIG. 4.
When the ink channel 131B in the array is selected according to desired print data, for example, a driving electric field is generated between the metal electrodes 111A and 111B and between the metal electrodes 111C and 111D. A positive electric potential such as 30V is applied to the metal electrodes 111A and 111D, and a negative electric potential such as -30V is applied to the metal electrodes 111B and 111C. The driving electric field is then generated on the side wall 102B in the direction from the metal electrode 111A to the metal electrode 111B, while the driving electric field is generated on the side wall 102C in the direction from the metal electrode 111D to the metal electrode 111C. As the driving electric field direction generated on the side wall 102B and the side wall 102C and the polarizing direction of the piezoelectric ceramic plate 101 are perpendicular to each other, the side wall 102B and the side wall 102C are deformed in the internal direction of the ink channel 131B by a piezoelectric thickness slip effect.
This deformation causes a decrease in volume of the ink channel 131B to result in an increase in ink pressure in the ink channel 131B. Accordingly, an ink droplet in the ink channel 131B is jetted from the jet nozzle 142. When the application of the electric potential is stopped, the side walls 102B and 102C return to their original positions before deformation, so that the ink pressure in the ink channel 131B is decreased, and ink is supplied from an ink supply section (not shown) into the ink channel 131B.
The manufacturing method of the above-mentioned array is explained briefly. First, the piezoelectric ceramic plate 101 having a plurality of grooves 103 is manufactured by the following method. As shown in FIG. 5, the piezoelectric ceramic plate 101 polarized in the direction of an arrow 151 is machined by grinding or the like, such as by rotation of a diamond cutting disk to form a plurality of parallel grooves 103 comprising the above-configured ink channels 131A-D.
Next, the above-mentioned metal electrodes 111A-D are formed on a side surface of each groove 103 by a well-known sputtering method.
Further, the cover plate 121 is bonded to an upper surface 104A of the piezoelectric ceramic plate 101 by the adhesive layer 112. The adhesive layer 112 includes epoxy adhesive and exhibits elasticity. The plurality of ink channels 131A-D are then defined by each groove 103 and the cover plate 121.
Lastly, the nozzle plate 141 having a plurality of jet nozzles 142 at positions corresponding to end positions of the ink channels 131A-D is bonded to an end surface 104B of the piezoelectric ceramic plate 101 on the ink jet side.
However, in this type of the ink droplet jet device, fine grooves must be made on the piezoelectric ceramic plate for forming a plurality of ink channels, in order to obtain an image of a high resolution formed by the jetted ink droplets. For that purpose, the interval between adjoining ink channels must be very small and a number of jet nozzles formed in the nozzle plate must be increased, causing a complicated grooving of the piezoelectric ceramic plate and, accordingly, increasing a manufacturing cost. Further, the conventional groove forming method has a limitation in a width and a distance between centers of the grooves which can be formed. Therefore, only an image of low resolution can be obtained in using the conventional droplet jet device.